1. Field of the Invention
This invention relates to a mechanism which enables the operator of a photo interpretation instrument to move a stereoscope from its normallY fixed position directly over the photograph(s) supported and illuminated by a light table to a second position which permits the operator to view the photographs with the unaided eye.
2. Description of the Prior Art
The process of interpreting or inspecting aerial photographs typically requires the use of instrumentation including a light table for supporting and illuminating the photographs, and appropriate viewing optics, such as a stereoscope, which is supported above the light table. The stereoscope typically includes a pair of rotatable rhomboid arms attached thereto. The photographs being studied are supported upon a flat translucent surface provided on the light table. In some instances, the photographs may be moved, as necessary, across the translucent surface from a supply roll to a take up roll. The Bausch & Lomb Zoom 240.TM. and Zoom 500.TM. image analysis systems are examples of such instrumentation.
By monoviewing one of a pair of stereo photographs through the optics of one of the rhomboid arms of the stereoscope, the operator determines where on a particular frame of the film the desired area to be inspected is located. By monoviewing through the optics of the other rhomboid arm, the adjacent (stereo) photo is similarly inspected. When the operator is satisfied that the desired areas of the stereo pair of photographs are similarly positioned, the instrument is switched from a mono mode to stereo. The operator is now able to analyze the pair of photos in stereo.
Many times during the examination and study of the selected area on the photographs, it becomes necessary for the operator to view the photos without the aid of the stereoscope. When utilizing a system which permits movement of the stereoscope in both x and y directions relative to the light table, the operator merely pushes the stereoscope to a remote location to directly view either one or both of the stereo pair of photos. However, in order to resume microscopic examination of the previously examined areas of the photos, the operator must manually relocate the stereoscope exactly over the prior location. This can be a time consuming and laborious task.
Should the operator be inspecting photos with the aid of an instrument having fairly high magnification, the task of direct, unaided viewing becomes quite onerous as the stereoscope is fixed to the table and the rhomboid arm's objectives are positioned immediately above the photos. It is, therefore, necessary to move the film from under the stereoscope in order to view the desired areas. The higher the magnification, the more difficult this becomes as the areas being examined represent a very small portion of the photograPh which makes repositioning those specific areas under the stereoscope in exactly the same position as before quite difficult. This is due to the fact that the operator may not be readily able to tell, once, the photo is moved, exactly where on the photo the desired area is located.
Other types of photogrammetric viewing instruments, which involve movement of the stereoscope with respect to the light table, are shown in U.S. Pat. Nos. 2,692,531 issued Oct. 26, 1954 to E. N. Waterworth et al and in 3,267,798 issued Aug. 23, 1966 to G. L. Hobrough et al. The Waterworth et al device shows a stereoscope mounted to a frame which is adjustable in the x and y-directions relative to the light table. The stereoscope is further mounted to a supPort beam by way of a parallel link mechanism which allows additional movement in the z-direction. When it becomes necessary for the operator to view the stereo pair of photos without the aid of the stereoscope, it must be moved from one position to another, either by sliding it in the x or y-directions, or by raising it in the z-direction. As no means are provided on the instrument to ensure exact repositioning, it is evident that refocusing is required.
The device shown in the Hobrough et al patent discloses a stereoscopic viewing station that is supported above a viewing table by way of pivotable arms which may be utilized to either raise or lower the stereoscope. This device is similar to the Waterworth et al instrument as the stereoscope must be refocused frequently when it is moved from one position to another with respect to the viewing table.
It will, therefore, be appreciated that a mechanism which would enable an operator to stereoscopically view stereo pairs of photos supported on a photogrammetric light table and then move the stereoscope, so that the photos may be manually viewed, and to then exactly reposition the stereoscope to resume microscopic examination of the precise area previously viewed is desirable. The apparatus of the present invention, provides such a mechanism.